44 
EVIDENCES OF SEPARATION. 
duced from actual explorings made at the 
edges of the sti*ata, but from an examination 
of their constitution. Many hard rocks are 
formed of gravel or sand^ the worn down 
fragments of pre-existing rocks. The old 
red sandstone contains pebbles of the rock 
on which it rests; the new red sandstone 
contains pebbles of the old red; the upper 
gravel include pebbles of both these, and of 
the chalk lying between them, but this order 
is never found to be reversed, we never 
find pebbles of chalk in the red sandstone ; 
and hence we have the same kind of assu¬ 
rance that the strata were successively 
and separately consolidated, as we have 
that the pebble beach of our coast is of sub¬ 
sequent origin as a whole, to the cliffs 
whence its fragments fell. 
The chief interest of modern geology is 
derived from the indisputable fact, that the 
solid strata of the earth are eharaeterized 
by peculiar fossil organic remains, that each 
one has its own distinct cabinet of botany 
and zoology. 
The investigation of organic remains has 
now taken the place of former speculative 
